The present invention relates to systems and methods that use virtual reality, augmented reality, and/or a synthetic computer-generated 3-dimensional information (VR/AR/synthetic 3D) for the measurement of human ocular performance. Examples of human ocular performance measurements that can be measured using VR/AR/synthetic 3D include vestibulo-ocular reflex, saccades, visual pursuit tracking, nystagmus, vergence, eye-lid closure, dynamic visual acuity, kinetic visual acuity, retinal image stability, foveal fixation stability, and focused position of the eyes.
1. Definitions. The definitions that follow apply to the terminology used in describing the content and embodiments in this disclosure and the related claims.
Virtual reality (VR) can be defined as a computer-generated simulation of a three-dimensional image or environment that can be explored and interacted with by a user. The user becomes part of the virtual scene or immersed within the environment. While being part of the virtual environment, he or she can interact within a seemingly real or physical way, to use or manipulate objects or special electronic equipment. An example would be to perform a series of actions with a device or use a glove fitted with sensors or to wear a helmet with a projected virtual screen inside. Virtual reality environments can be implemented stereoscopically using an opaque display system, i.e. the user only sees the virtual scene and cannot see through the scene. The peripheral vision can be blocked to decrease any distraction from the user experience. Virtual reality can be used in simulators. Virtual display images or visual elements may be actively streamed from an attached computer, a wireless computer source, a smartphone, a smart display pad, or directly with digital camera systems and virtual camera systems. Virtual reality can also be created using holographic or volumetric three-dimensional displays.
Augmented reality (AR) can be defined broadly as the integration of digital information with the user's environment in real time. It refers to technology that incorporates real-time inputs from the existing world to create an output that combines both real-world data and some programmed, interactive elements that operate on those real-world inputs. Augmented reality will respond contextually to new external information and account for changes to users' environments, interpret gestures and actions in real time, with minimal to no explicit commands from users and will be presented in a way that does not restrict users' movements in their environment. It overlays information on an image being viewed through a device. Unlike virtual reality, which creates a totally artificial environment, augmented reality uses the existing environment and overlays new information on top of it.
A synthetic computer-generated 3-dimensional information (synthetic 3D) is a computer generated 3D model of visual information or images on a plane with X, Y and Z axes. A synthetic 3D model could be rotated and viewed from any angle. Synthetic objects don't need to exist in nature. These objects could be totally synthetic or partially synthetic. These objects or images can be realistic three-dimensional representations of the outside world. Synthetic 3D information can include integrated guidance symbologies. 3D synthetic information can be static and/or dynamic.
A display can be defined as a device that presents characters, images, or graphics representing data in a computer memory. Displays can present visual information in two dimensions or in three dimensions. In this document a three-dimensional display (3D display) is a display that conveys depth perception information to a user. 3D displays can be holograms, volumetric displays, or can use other technologies for presenting depth information in combination with the traditional two-dimensional information, such as stereoscopic displays. Examples of volumetric displays can include: multiplanar displays that have multiple display planes stacked up; and rotating panel displays where a rotating panel sweeps out a volume.
A stereoscopic display is a display system that presents offset 2D images separately to the left and right eye. Both of these 2D offset images are then combined in the brain to give the perception of 3-dimensional depth. Examples of stereoscopic display technologies and devices can include:                (a) Presenting a left eye image and a right eye image on separate screens in a head-worn unit.        (b) Presenting a left eye image and a right eye image on a single display and having the user wear glasses that separate the left-eye image and the right eye image. Examples of technologies that can be used for this image separation are color filters, polarizing filters, and time-dependent shutters that open for one eye when a left image is being presented on the display and open for the other eye when the right image is being displayed.        (c) A lenticular display that presents the images for the left eye and right eye in a unit that is not worn by the user. Instead the image for the left eye and the right eye are produced by a single device in a way that causes the left image to be projected at an angle visible to the left eye and causes the right image to be projected at an angle visible to the right eye.        
Holograms can be described generally as three-dimensional images that do not require any structure worn by a user for the display of the 3D image to a user. A hologram is physical structure that diffracts light into an image. The term ‘hologram’ can refer to both the encoded material and the resulting image. It can be described as a photographic recording of a light field, rather than of an image formed by a lens, and it is used to display a fully three-dimensional image of the holographed image or object. The hologram itself is not an image and it is usually unintelligible when viewed under diffuse ambient light. It is an encoding of the light field as an interference pattern of seemingly random variations in the opacity, density, or surface profile of the photographic medium. When suitably lit, the interference pattern diffracts the light into a reproduction of the original light field and the objects that were in it appear to still be there, exhibiting visual depth cues such as parallax and perspective that change realistically with any change in the relative position of the observer. In its pure form, holography requires the use of laser light for illuminating the subject and for viewing the finished hologram. A holographic display can have the ability to address all four of the following eye mechanisms: binocular disparity; motion parallax; eye accommodation; and eye convergence. In a holographic display, the 3D objects can be viewed without wearing any special glasses and no visual fatigue will be caused to human eyes.
Vestibulo-ocular reflex (or VOR) refers to the ocular (e.g. human visual motor system) response to stimulus of the vestibular (e.g. inner ear) system, in which the eye movement response is caused by head movement. More specifically, VOR is an involuntary movement of the eyes in response to rotational movements of the head detected by the inner ear balance system. As will be described further in this disclosure, measures of VOR can include gain, phase, symmetry, and saccadic responses to head movements at various frequencies. The VOR stabilizes the visual image on the back of the eye (retina) during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field (e.g. on the fovea). This allows a person to visualize objects clearly during brief head movements. A simplistic view of the VOR involves a 3-neuron arc that consists of the vestibular ganglion, vestibular nuclei, and oculomotor nuclei. When the head moves, the VOR responds with an eye movement that is equal in magnitude but opposite in direction. For example, when the head moves to the right, the eyes move to the left and when the head moves up the eyes move downward. Head movements, rotational and translational, stimulate the VOR. With a rotational movement, the head moves relative to the body. Examples of this include turning the head back and forth, nodding, and bringing the ear in contact with the shoulder. Translational movements occur when the entire body, including the head, is moved in tandem. Translational movements may occur when an individual stands on a moving sidewalk. Thus, rotational VOR responds to angular motion of the head and results from stimulation of the semicircular canals, whereas translational VOR responds to linear motion of the head and results from stimulation of the otolithic organs. Some head movements may involve a combination of both translational VOR and rotational VOR. The VOR is a reflex that acts at short latency to generate eye movements that compensate for head rotations in order to preserve clear vision during locomotion. The VOR is the most accessible gauge of vestibular function. Evaluating the VOR requires application of a vestibular stimulus and measurement of the resulting eye movements. For example, when the head moves to the right, the eyes move to the left, and vice versa. The VOR normally serves to stabilize gaze in space during head movements by generating equal and opposite compensatory eye movements. The VOR has both rotational and translational aspects. When the head rotates about any axis (horizontal, vertical, or torsional) distant visual images are stabilized by rotating the eyes about the same axis, but in the opposite direction. When the head translates, for example during walking, the visual fixation point is maintained by rotating gaze direction in the opposite direction, by an amount that depends on distance. Eye movements generated by the human VOR system are intended to stabilize the image on the retina and specifically on the fovea during brief, non-sustained head movements. In order to see the surrounding world clearly, the retinal images on the fovea must remain stable, within certain margins. Stability is affected, however, by the continuous movements of the head, which may cause motion blur. In order to prevent motion blur, head movements are counter-balanced by compensatory eye movements. These are mediated by two reflexes, the VOR, which senses head rotations in the labyrinth, and the optokinetic reflex (OKR), which directly senses visual image motion. Vestibulo-ocular eye movements that reflexively occur in the direction opposite a head movement can also be included within eye signal controls during voluntary head movements. Measurement of the VOR is related to the semicircular canal being tested in the direction of the motion of the head movement. This most often includes both vertical and horizontal VOR tests. Eye-velocity response to the head-velocity stimulus can be seen with the VOR gain for the two directions of rotation and overt and covert saccades can also be identified and measured. During VOR testing, if the person's vestibulo-ocular response is abnormal, then their eyes will be taken off target during the head rotation, because their eyes will not rotate at the correct speed to exactly compensate for head rotation. In this instance, an abnormal VOP means that the eyes can move with the head during a passive unpredictable head turn and will be taken off target by the head turn, so that at the end of the head turn the person must make a corrective saccade toward the target.
A saccade is a fast movement of an eye, head or other part of the body or of a device. It can also be a fast shift in frequency of an emitted signal or other quick change. Saccades are quick, simultaneous movements of both eyes in the same direction. Humans do not look at a scene in fixed steadiness, the eyes move around, locating interesting parts of the scene and building up a mental, three-dimensional ‘map’ corresponding to the scene. When scanning the scene in front of you or reading these words right now, your eyes make jerky saccadic movements and your eyes stop several times, moving very quickly between each stop. We cannot consciously control the speed of movement during each saccade; the eyes move as fast as they can. One reason for the saccadic movement of the human eye is that the central part of the retina (known as the fovea) plays a critical role in resolving objects. By moving the eye so that small parts of a scene can be sensed with greater resolution, body resources can be used more efficiently. The saccade that occurs at the end of a head turn with someone who has an abnormal VOR is usually a very clear saccade, and it is referred to as an overt saccade. An overt saccade is indicative of abnormal semicircular canal function on the side to which the head was rotated. For example, an overt saccade after a leftwards head rotation means the left semicircular canal has a deficit. Covert saccades are small corrective saccades that occur during the head movement of a person with abnormal inner ear function. Covert saccades reduce the need for overt saccades that the end of the head movement and are more difficult to identify than overt saccades. Covert saccades are very fast. This makes them almost impossible to detect by the naked eye, and therefore sensitive eye tracking measurements are typically required to detect covert saccades. There is a rapid deceleration phase as the direction of sight lands on the new target location. Following a very short delay, large saccades are frequently accompanied by at least one smaller corrective saccade to further approach a target location. Corrective saccades can occur even if the target has been made to disappear, further supporting the projected, ballistic nature of saccadic movements. However, corrective saccades are more frequent if the target remains visible.
Accuracy, amplitude, latency and velocity can be measured with oculomotor eye movements, most commonly with saccades, vergence, smooth pursuit, and vestibulo-ocular movements. Saccades can be elicited voluntarily, but occur reflexively whenever the eyes are open, even when fixated on a target. They serve as a mechanism for fixation, rapid eye movement, and the fast phase of optokinetic nystagmus. The rapid eye movements that occur during an important phase of sleep are also saccades. After the onset of a target appearance for a saccade, it takes about 200 ms for eye movement to begin. During this delay, the position of the target with respect to the fovea is computed (that is, how far the eye has to move), and the difference between the initial and intended position, or “motor error” is converted into a motor command that activates the extraocular muscles to move the eyes the correct distance in the appropriate direction. The latency, amplitude, accuracy and velocity of each respective corrective saccade and latency totals and accuracy can be calculated.
Saccade accuracy refers to the eye's ability to quickly move and accurately shift from one target fixation to another. Saccade adaptation is a process for maintaining saccade accuracy based on evaluating the accuracy of past saccades and appropriately correcting the motor commands for subsequent saccades. An adaptive process is required to maintain saccade accuracy because saccades have too short a duration relative to the long delays in the visual pathways to be corrected while in flight.
Saccade amplitude—refers to the size of the eye movement response, usually measured in degrees or minutes of arc. The amplitude determines the saccade accuracy. This is sometimes denoted using “gain”. It is also described as the angular distance the eye travels during the movement. For amplitudes up to 15 or 20°, the velocity of a saccade linearly depends on the amplitude (the so-called saccadic main sequence). Saccade duration depends on saccade amplitude. In saccades larger than 60 degrees, the peak velocity remains constant at the maximum velocity attainable by the eye. In addition to the kind of saccades described above, the human eye is in a constant state of vibration, oscillating back and forth at a rate of about 60 Hz.
Saccade velocity—this is the speed measurement during the eye movement. High peak velocities and the main sequence relationship can also be used to distinguish micro-/saccades from other eye movements like (ocular tremor, ocular drift and smooth pursuit).
Saccade latency—this is the time taken from the appearance of a target to the beginning of an eye movement in response to that target. Disorders of latency (timing) can be seen with saccades, VOR and visual pursuit.
Saccadic Inhibition. Studies of eye movements in continuous tasks, such as reading, have shown that a task-irrelevant visual transient (for example a flash of a portion of the computer display) can interfere with the production of scanning saccades. There is an absence or near-absence of saccades initiated around 80-120 ms following the transient. This inhibitory effect (termed saccadic inhibition SI) is also observed in simple saccade experiments using small visual targets and it has been suggested that SI may be similar to, or underlie, the remote distractor effect.
Visual pursuit means the movement of the eyes in response to visual signals. Smooth pursuit eye movements allow the eyes to closely follow a moving object. It is one of two ways that humans and other visual animals can voluntarily shift gaze, the other being saccadic eye movements. Pursuit differs from the VOR, which only occurs during movements of the head and serves to stabilize gaze on a stationary object. Most people are unable to initiate pursuit without a moving visual signal. The pursuit of targets moving with velocities of greater than 30°/s tend to require catch-up saccades. Most humans and primates tend to be better at horizontal than vertical smooth pursuit, as defined by their ability to pursue smoothly without making catch-up saccades. Most humans are also better at downward than upward pursuit. Pursuit is modified by ongoing visual feedback. Smooth pursuit is traditionally tested by having the person follow an object moved across their full range of horizontal and vertical eye movements.
Visual pursuit tracking can be defined as measuring a person's eye movement ability to match a visual element or target of interest movement. Visual pursuit eye movements utilize some of the vestibulo-ocular reflex pathways and require a visual input to the occipital cortex in order to permit locking of the eyes onto a visual element or target of interest. Pursuit movements are described to be voluntary, smooth, continuous, conjugate eye movements with velocity and trajectory determined by the moving visual target. By tracking the movement of the visual target, the eyes maintain a focused image of the target on the fovea. A visual stimulus (the moving visual target) is required to initiate this eye movement. Pursuit gain, which is the ratio of eye velocity to target velocity, is affected by target velocity, acceleration and frequency. Visual pursuit tracking may be related to factors that are difficult to quantify, such as the degree of alertness present in persons, visual acuity or the visibility of the pursuit target. Visual pursuit tracking can be decayed with alcohol, centrally acting medications such as anticonvulsants, minor tranquilizers, preparations used for sleep. It is also clear that visual pursuit performance declines with age and can be adversely affected by vestibular dysfunction, central nervous system disorders and trauma, such as concussions and traumatic brain injury (TBI).
Visual pursuit accuracy is defined by the ability of the eyes to closely follow a moving object. The pursuit of targets moving with velocities of greater than 30°/s tends to require catch-up saccades. Smooth pursuit accuracy, represents how closely the percentage of time the smooth pursuit velocity value remains within the target velocity value.
Visual pursuit movements are much slower tracking movements of the eyes designed to keep the moving stimulus on the fovea. Such movements are under voluntary control in the sense that the observer can choose whether to track a moving stimulus. Although it may appear that our eyes are not moving when we fixate an object, in fact they are in continual small-scale motion, showing irregular drift and tremor, interspersed by miniature saccadic movements (less than 0.5 degrees). These fixational eye movements are essential to prevent our visual percept from fading. Pursuit consists of two phases—initiation and maintenance. Measures of initiation parameters can reveal information about the visual motion processing that is necessary for pursuit.
Visual pursuit acceleration—this is the rate of change of the eye velocity. The first approximately 20 milliseconds of pursuit tends to be the same regardless of target parameters. However, for the next 80 milliseconds or so, target speed and position has a large effect on acceleration.
Visual pursuit velocity—After pursuit initiation, speed of the eye movement (velocity) usually rises to a peak and then either declines slightly or oscillates around the target velocity. This peak velocity can be used to derive a value for gain (peak velocity/target velocity). It is usually near the velocity of the target. Instead of using peak velocity, it is also sometimes of interest to use measures of velocity at particular times relative to either target appearance or pursuit initiation. Eye velocity up to 100 milliseconds after target appearance can be used as a measure of prediction or anticipation. Velocity measured 100 milliseconds after pursuit begins reveals something about the ability of pursuit system in the absence of visual feedback.
Visual pursuit latency—is defined by the time from target appearance to the beginning of pursuit. The difficulty here is defining when pursuit begins. Usually it is measured from traces of eye velocity. It is often calculated by finding the intersection between two regression functions one fitted to velocity about the time of target appearance, and the second fitted over the initial part of the pursuit response.
Nystagmus is a description of abnormal involuntary or uncontrollable eye movement, characterized by jumping (or back and forth) movement of the eyes, which results in reduced or limited vision. It is often called “dancing eyes”. Nystagmus can occur in three directions: (1) side-to-side movements (horizontal nystagmus), (2) up and down movements (vertical nystagmus), or (3) rotation of the eyes as seen when observing the front of the face (rotary or torsional nystagmus).
Vergence is the simultaneous movement of both eyes in opposite directions to rapidly obtain or maintain single binocular vision or ocular fusion, or singleness, of the object of interest. It is often referred to as convergence or divergence of the eyes, to focus on objects that are closer or further away from the individual. The maintain binocular vision, the eyes must rotate around a vertical axis so that the projection of the image is in the center of the retina in both eyes. Vergence measurements can easily be performed. Normally, changing the focus of the eyes to look at an object at a different distance will automatically cause vergence and accommodation, known as accommodation-convergence reflex. Convergence is the simultaneous inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision when viewing an object. Vergence tracking occurs in the horizontal, vertical, and/or cyclorotary dimensions. Vergence requires that the occipital lobes be intact and the pathway involves the rostral midbrain reticular formation (adjacent to the oculomotor nuclei) where there are neurons that are active during vergence activities. It comprises a complex and finely tuned interactive oculomotor response to a range of sensory and perceptual stimuli. There is an important interaction between the vergence system and vestibular (inner ear balance) system. In order to keep the eyes focused on a visual element or object of interest, while the head is moving, the vestibular system senses head rotation and linear acceleration, and activates the eyes to counterrotate so as to keep gaze constant even though the head is moving. As an example, this is what enables us to see a tennis ball while moving our head. The problem becomes more difficult at near vision, because the eyes are not located at the center of rotation of the head, but rather are about 10 cm anterior to the axis of rotation. Therefore, when a person is focused on a near target (such as 10 cm away), the amount of eye movement needed to keep the target fixated is much greater than the amount needed to view a similar object 100 cm away. This additional eye movement is supplied by the otoliths (linear acceleration sensors) that produce eye movement that are roughly inversely proportional to the distance of the target from the center of the eye. Persons with disorders of their otoliths, might reasonably have a selective problem with stabilizing their vision while the head is moving, at near vision. Vergence can be also be adversely affected by other factors including aging, visual abnormalities, concussion and traumatic brain injury (TBI).
Eyelid closure refers to the distance between the margins of the upper and lower eyelid and is often measured by palpebral fissure height, marginal reflex distance, levator function and upper eyelid crease. The palpebral fissure height (PF) is the distance between the upper and lower eyelid margins at the axis of the pupil. Normal measurement is 9 to 12 mm defined as being either voluntary or involuntary eye-lid movement. Marginal reflex distance (MRD) is the distance between the central corneal light reflex and upper eyelid margin with eyes in primary position. The severity of ptosis is better determined with MRD than PF measurements as lower lid malpositions are eliminated. Normal MRD is 4-5 mm. Levator function is measured as the distance in millimeters (mm) of the upper lid margin when looking downward and when looking upward. Upper eyelid crease position is the distance from the upper eyelid crease to the eyelid margin. It is normally 7-8 mm in males and 9-10 mm in females.
The eyelids act to protect the anterior surface of the globe from local injury. Additionally, they aid in regulation of light reaching the eye; in tear film maintenance, by distributing the protective and optically important tear film over the cornea during blinking; and in tear flow, by their pumping action on the conjunctival sac and lacrimal sac. The closure of the eyelids is facilitated by the protractors of the eyelids: circumferential orbicularis oculi muscle, which is innervated by the facial (seventh cranial) nerve. The elevators of the upper eyelid are the levator palpebrae superioris and the Muller's muscle. The levator palpebrae superioris is the main upper eyelid elevator and is innervated by the oculomotor (third cranial) nerve. The Muller's muscle is a smooth muscle that arises from the undersurface of the levator and inserts into the superior tarsus. The Muller's muscle is innervated by the sympathetic nervous system. The muscle is responsible for the over-elevation of the eyelid when a patient becomes excited or fearful and leads to mild ptosis with fatigue or inattention.
Active movements related to eye-lid closure can be referred to as eyelid contractions, twitches or blinks and can occur spontaneously, reflexively, or voluntarily. Spontaneous blinking which is done without external stimuli and internal effort. This type of blinking is conducted in the pre-motor brain stem and happens without conscious effort. A reflex blink occurs in response to an external stimulus, such as contact with the cornea or objects that appear rapidly in front of the eye. A reflex blink is not necessarily a conscious blink either; however, it does happen faster than a spontaneous blink. Reflex blink may occur in response to tactile stimuli, optical stimuli or auditory stimuli. Voluntary blink is larger amplitude than Reflex blink, with the use of all 3 divisions of the orbicularis oculi muscle. Generally, between each blink is an interval of 2-10 seconds; actual rates vary by individual averaging around 10 blinks per minute in a laboratory setting. However, when the eyes are focused on an object for an extended period of time, such as when reading, the rate of blinking decreases to about 3 to 4 times per minute. This is the major reason that eyes dry out and become fatigued when reading. Blinks affect not only horizontal saccades but also vertical saccades, vergence eye movements, and saccade-vergence interaction in humans. While the saccade and vergence duration is increased during blinks, the peak velocity, acceleration and deceleration is decreased. In contrast, the amplitude of saccades and vergence does not appear to change during blinks. Blinks during gaze straight ahead elicited an eye movement toward the nose and downward. Blinks have a maximum effect when elicited ˜100 ms before eye movements. All blink-elicited eye movements started with the blink onset but were completed before the end of the blink. Blink speed can be affected by elements such as fatigue, eye injury, medication, and disease. For example, blepharospasm is any abnormal contraction or twitch of the eyelid. In most cases, symptoms last for a few days then disappear without treatment, but sometimes the twitching is chronic and persistent, causing lifelong challenges.
Apraxia of eyelid opening is a condition in which patients who have otherwise normal eyelids have difficulty opening the eyelids. Pure apraxia of lid opening (which is not associated with blepharospasm) is very rare. However, apraxia of lid opening is commonly associated with blepharospasm.
Visual acuity (VA) refers to acuteness or clearness of vision, which is dependent on optical and neural factors, i.e., (i) the sharpness of the retinal focus within the eye, (ii) the intactness and functioning of the retina, and (iii) the sensitivity of the interpretative faculty of the brain. A Snellen chart (eye chart that uses block letters arranged in rows of various sizes) is frequently used for visual acuity testing and measures the resolving power of the eye, particularly with its ability to distinguish letters and numbers at a given distance as well as the sharpness or clearness of vision.
The dynamic visual acuity (DVA) can be used interchangeably with kinetic visual acuity (KVA) as they both have the same meaning. In this document, DVA will be used to assess impairments in a person's ability to perceive objects accurately while actively moving the head, or the ability to track a moving object. It is an eye stabilization measurement while the head is in motion. In normal individuals, losses in visual acuity are minimized during head movements by the vestibulo-ocular system that maintains the direction of gaze on an external target by driving the eyes in the opposite direction of the head movement. When the vestibulo-ocular system is impaired, visual acuity degrades during head movements. The DVA is an impairment test that quantifies the impact of the vestibulo-ocular system pathology on a user's ability to maintain visual acuity while moving. Information provided by the DVA is complementary to and not a substitute for physiological tests of the VOR system. The DVA quantifies the combined influences of the underlying vestibulo-ocular pathology and the person's adaptive response to pathology. DVA testing is sometimes obtained for those persons suspected of having an inner ear abnormality. Abnormalities usually correlate with oscillopsia (a visual disturbance in which objects in the visual field appear to oscillate or jump while walking or moving). Currently with DVA testing, worsening of visual acuity by at least three lines on a visual acuity chart (e.g., Snellen chart or Rosenbaum card) during head turning from side to side at 1 Hz or more is reported as being abnormal. In normal individuals, losses in visual acuity are minimized during head movements by the vestibulo-ocular system that maintains the direction of gaze on an external target by driving the eyes in the opposite direction of the head movement When the vestibular system is impaired, visual acuity degrades during head movements. Individuals with such ocular performance deficits can improve their dynamic acuity by performing rapid “catch-up” saccadic eye movements and/or with predictive saccades.
Dynamic visual stability (DVS) and retinal image stability (RIS) can be used interchangeably. In this document, DVS will be used to describe the ability to visualize objects accurately, with foveal fixation, while actively moving the head. When the eye moves over the visual scene, the image of the world moves about on the retina, yet the world or image observed is perceive as being stable. DVS enables a person to prevent perceptual blurring when the body moves actively. The goal of oculomotor compensation is not retinal image stabilization, but rather controlled retinal image motion adjusted to be optimal for visual processing over the full range of natural motions of the body or with head movement. Although we perceive a stable visual world, the visual input to the retina is never stationary. Eye movements continually displace the retinal projection of the scene, even when we attempt to maintain steady fixation. Our visual system actively perceives the world by pointing the fovea, the area of the retina where resolution is best, towards a single part of the scene at a time. Using fixations and saccadic eye movements to sample the environment is an old strategy, in evolutionary terms, but this strategy requires an elaborate system of visual processing in order to create the rich perceptual experience. One of the most basic feats of the visual system is to correctly discern whether movement on the retina is owing to real motion in the world or rather to self-movement (displacement of our eyes, head or body in space). The retinal image is never particularly stable. This instability is owing to the frequent occurrence of tremors, drifts, microsaccades, blinks and small movements of the head. The perceptual cancellation of ocular drift appears to primarily occur through retinal mechanisms, rather than extra-retinal mechanisms. Attention also plays a role in visual stability, most probably by limiting the number of items that are fully processed and remembered.
Foveal Fixation Stability (FFS) refers to the ability to maintain an image on the fovea, which is crucial for the visual extraction of spatial detail. If the target image moves 1° from foveal center, or if random movement of the image on the fovea exceeds 2°/sec, visual acuity degrades substantially. Either of these conditions may occur if deficiencies in oculomotor control compromise the ability to maintain target alignment within these limits. Many aspects of oculomotor function do change with age. For example, smooth pursuit movements slow with age, and the range of voluntary eye movements becomes restricted, especially for upward gaze. DVA, FFS, and the vestibulo-ocular reflex decline with age.
Focused position of the eyes can be defined as the position or orientation of the eyes to provide a clear image of a visual element or target of interest on the fovea.
2. Limitations of the Prior Art for a Non-Clinical Environment
Prior art systems for tracking head and eye movements have serious limitations due to the bulkiness of the equipment being used and the high number of the components required. Prior art systems for tracking eye movement include electro-oculography, magnetic scleral search coils, infrared video-nystagmography, and other video eye-tracking devices requiring umbilical attachments to computer systems and light bars or laser pointing systems for eye focusing. Some also utilize solid lights (such as “dots”) without specific features to enable a person to focus upon. Additionally, prior art utilizes only two-dimensional images for the person to visualize. Some systems only test one (1) eye, making the measurement of ocular movements and reflexes less accurate. Testing with some prior art systems and methods has little complexity features, has not advanced with available technology and cannot provide images or visual scenes familiar to the person's life activities. These prior art techniques do not allow for more robust and more accurate testing of human ocular performance.
Current clinical eye response measuring equipment is highly specialized, bulky and requires multiple pieces of equipment in a dedicated laboratory. There is need to have a more advanced and robust system and method of measuring human ocular performance. The use of VR/AR/synthetic 3D can greatly advance the measurement of human ocular performance with the potential for helping a person improve his/her ocular performance. Systems and methods incorporating VR/AR/synthetic 3D can be more accurate, by measuring the movements of both eyes with head tracking and can provide a variety of features to the visual elements or targets of interest for the individual to focus upon. Having a stronger visual element can enhance the visual fixation ability during the test being performed on the individual and can improve test accuracy. The use of VR/AR/synthetic 3D can provide unique complexity to the visual elements and to the background scenes to make a more engaging testing environment.
It should be understood that the drawings are not necessarily to scale. In certain instances, details that are not necessary for an understanding of the invention or that render other details difficult to perceive may have been omitted. It should be understood that the invention is not necessarily limited to the particular embodiments illustrated herein.